Optics letters最新文献

The accelerated advancement of high-energy laser technology has resulted in an increased necessity for multifunctional laser protection. Herein, we present an investigation into a static visible and dynamic 1064 nm laser protection window. Through studying the photonic crystal energy band structure and topological interface state properties, both 66.49% average visible light transmittance and 84.01% low-energy 1064 nm laser transmittance are achieved. The combination of a large third-order nonlinear effect of LiNbO₃ and strong light field localization of a topological interface state enables a 27.54 mJ/cm² protection threshold below that of traditional materials. This study offers what we believe to be new avenues for the development of multifunctional optical windows and novel optical elements.

Transverse modulation instability (MI) has been proved useful for reconstructing noisy images. However, the signal-noise resonances for high-frequency modes are always suppressed during the generation of instability, resulting in the blurring of output images. By controlling of photo-birefringence and isomerization of azobenzene-derivative polymer, we proposed an instability-driven reconstruction by re-growing high-frequency modes via localizing wave response. The agreement between the experimental results and numerical simulations proves its effectiveness. This work provides a general and flexible way for high-resolution target detection.

Parallel generation of multi-channel chaos is critical to applications, and the key challenge is the simultaneous generation of broadband chaos with multiple channels and low correlation. Here, we experimentally demonstrate a parallel broadband chaos generation scheme using a single long-active-cavity Fabry-Perot (LC-FP) semiconductor laser under optical feedback. The active-cavity length is designed to be 1500 μm, so the power spectrum of chaos is expanded and flattened by the mode-beating effect. The experimental result shows that all-mode chaos with a bandwidth of 33.76 GHz and a spectrum flatness of ±2.5 dB is obtained. Furthermore, eight-channel chaotic signals with bandwidth larger than 27 GHz and correlation coefficients smaller than 0.1 are parallelly generated using optical filtering, where the spectrum flatness is about ±4 dB.

Overcoming the challenge of preparing high-transparency and low-resistivity thin films is of great significance for the development of indium-free transparent electrodes. In the present work, high-quality Mg, Al, and Ga co-doped ZnO (MAGZO)/Cu/MAGZO multilayer thin films are deposited on glass by magnetron sputtering. The effects of Cu layer thickness (d _Cu) on the structural, morphological, optical, and electrical characteristics of the films are investigated in detail. With increasing d _Cu from 0 to 25 nm, the growth orientation of (002) ZnO crystal weakens, while that of (111) Cu crystal strengthens, and the surface of the films exhibits uniform, low roughness, and defect-free characteristics. Additionally, both the resistivity and the optical transmittance generally decrease with increasing Cu layer thickness. Interestingly, the average visible transmittance has a reverse change as d _Cu increases from 5 to 11 nm, resulting in the optimal photoelectric performance of the multilayers at d _Cu= 11 nm: the figure of merit of 9.42 × 10^-3 Ω^-1 with the resistivity of 1.24 × 10^-4 Ω cm and the visible transmittance of 84.2%. Compared with other reported sandwich transparent conductive films, it is found that doping Mg in the oxide layer is the key to improving the overall optoelectronic properties of the multilayers.

An approach for generating phase-coded coherent microwave pulse trains at high frequencies is proposed and demonstrated based on an actively mode-locked optoelectronic parametric oscillator (AML-OEPO), where an electrical mixer is inserted into the cavity of an optoelectronic oscillator (OEO) to achieve both mode locking and parameter oscillation. The driving signal applied to the mixer is a low-frequency sinusoidal signal with voltage polarity coding, where the frequency is the same as the free spectral range (FSR) of the OEO cavity, and the duration of each voltage polarity coding bit is identical to the loop delay. As a result, phase-coded coherent microwave pulse trains can be generated, where the pulse interval is equal to the loop delay due to the active mode locking effect, and the phase coding period is equal to a multiple integer of the loop delay due to parameter oscillation. The enhancement of the signal period and the highly coherent characteristic are beneficial for breaking the contradiction between unambiguous detection range and ranging resolution in pulse radars. In the experiment, phase-coded microwave pulse trains with either 13-bit barker codes or 7-bit M codes are generated at 15.026 GHz. The autocorrelation calculation result of the phase-coded microwave pulse train with 13-bit barker codes shows a high peak-to-sidelobe ratio, verifying high coherence.

We present a spectroscopic method that employs a single linearly chirped laser pulse (LCLP) generated by external modulation to realize long-distance multi-point gas sensing. Even without frequency-chirping calibration, accurate single-shot spectral measurement is rendered possible by the high linearity of intrapulse chirping (linearity error of ∼10^-4). Utilizing the LCLP's built-in capacity of time-division-multiplexing, high measurement sensitivity is guaranteed by introducing a multichannel intensity noise compensation mechanism. As proof of concept, this method is experimentally demonstrated by three acetylene gas sensing nodes using an LCLP of 100-ns pulse width and 20-GHz chirping range, achieving a time resolution of 280 µs with 90-ppm sensitivity and a spatial resolution of 25 m over a 25-km sensing distance. Having the advantages of high time resolution, high spatial resolution, and accurate spectral measurement, our proposed method promotes a novel, to the best of our knowledge, way of developing spectroscopic gas sensing systems for challenging applications where spatially resolved gas analysis with fast response over a long distance is required.

We demonstrate an external cavity laser with intrinsic linewidth below 100 Hz around an operating wavelength of 852 nm, selected for its relevance to laser cooling and manipulation of cesium atoms. This system achieves a maximum CW output power of 24 mW, a wavelength tunability over 10 nm, and a side-mode suppression ratio exceeding 50 dB. This performance level is facilitated by careful design of a low-loss integrated silicon nitride photonic circuit serving as the external cavity combined with commercially available semiconductor gain chips. This approach demonstrates the feasibility of compact integrated lasers with sub-kHz linewidth centering on the needs of emerging sensor concepts based on ultracold atoms and can be further extended to shorter wavelengths via selection of suitable semiconductor gain media.

The intermediate phase produced by the complexation of metal ions and solvent molecules usually occurs in the crystallization process of perovskite single crystal or film. Effective in situ monitoring of intermediate-phase evolution is beneficial to the control of crystal quality. However, it is difficult to realize. In this work, infrared fiber evanescent wave spectroscopy (FEWS) was raised to monitor the intermediate-phase evolution in real time and non-destructively using GeAsSeTe chalcogenide optical fibers. The vibrational and rotational dynamics of specific molecular functional groups was operando captured, reflecting a perovskite precursor of different states. Taking BM₂PbBr₄ (BM = benzimidazole) perovskite as an example, the shift of the stretching vibration of -C=O groups in DMF (N,N-dimethylformamide) toward low wavenumbers and then recovered toward original position probed the complexion of Pb²⁺ and carbonyl groups into (DMF)₂BMPbBr₃ intermediate phase and then decomplexing to precipitate BM₂PbBr₄ perovskite crystal. Some anomalous emergence of new vibrational bands associating with -C-N and -N-H bonds suggest the variation of DMF-BMBr hydrogen bonds during intermediate-phase evolution. This technique provides new, to the best of our knowledge, insights into the control of perovskite crystallization processes and pushes the development of high-quality perovskite materials for high-performance photovoltaic or optoelectronic devices.

We produce families of two-dimensional gap solitons (GSs) maintained by moiré lattices (MLs) composed of linear and nonlinear sublattices, with the defocusing sign of the nonlinearity. Depending on the angle between the sublattices, the ML may be quasiperiodic or periodic, composed of mutually incommensurate or commensurate sublattices, respectively (in the latter case, the inter-lattice angle corresponds to Pythagorean triples). The GSs include fundamental, quadrupole, and octupole solitons, as well as quadrupoles and octupoles carrying unitary vorticity. Stability segments of the GS families are identified by means of the linearized equation for small perturbations, and confirmed by direct simulations of perturbed evolution.

Gallium nitride-based nanowires (NWs) overcome heteroepitaxy limits, enabling GaN-on-silicon devices, and offer high sensitivity for detection, sensing, and photocatalysis. Additional nanowire coating enhances their performance, protects against photoadsorption, and enables control over structural and optical properties. In this work, we investigate core-shell GaN-(Al/Hf)O_x nanowires, which meet the aforementioned expectations. We focus on reflectance, a fundamental optical parameter indicating structure applicability. We identified the proper dependence between reflectance spectra and shell composition and thickness, based on microscopic imaging, and adapted effective medium approximation. Finally, we expand upon a previous model, achieving great agreement between the simulation and the experimental data. Thus, we demonstrate how the description of complex nanostructures can be simplified and the composition of the nanowire ensemble can be estimated.